Forage harvesters are used in agriculture to harvest plants from a field, to chop them and to unload them by means of an adjustable transfer device onto a container of a transport vehicle that drives on a side of the forage harvester. The position of the adjustable transfer device, normally arranged in the form of a spout, can be controlled by an operator by means of inputs on a hydraulic handle and actuators, normally hydraulic cylinders, in order to move the adjustable transfer device into a position in which the crop is unloaded onto the container of the transport vehicle, but not onto the ground. Usually, the adjustable transfer device can be rotated around a vertical axis, tilted around a horizontal axis to adjust the height of its outer end, and an end flap can be rotated in order to define the exhaust direction of the crop.
Since the control of the adjustable transfer device is exhausting for the forage harvester operator, automatic solutions have been proposed for controlling the transfer device that use data on the relative position of the harvesting machine and the container, or a optical image capture device with an image processing system. The latter however are not always able to identify the container correctly, in particular when a field is opened, i.e. the forage harvester harvests a first strip of the field with standing crop on both sides such that the transport vehicle needs to follow the forage harvester, and the container to be filled is towed behind a tractor following the forage harvester, such that the distance between the forage harvester and the container is relatively large.